Basement insulation in a mixed-humid climate
1920s house in TN, heating-dominated climate. The house has a full basement, completely below-grade. The previous owner had 6″ batts installed in the basement ceiling, but no air sealing. Here’s my question: I’m going to remove the insulation so that I can Air Seal the entire area. Do I even need to reinstall the insulation after I’m done? It’s constantly 60-65 degrees down there, so it seems like conductive heat transfer would be minimum even without the insulation ( we keep the t-stat around 60 in the winter and 70 in the summer). I intend to insulate the rim joist after the air sealing is complete. Any thoughts would be appreciated.
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It sounds like you are in climate zone 4. The 2009 IRC requires basement wall insulation in your climate zone. If you are using rigid foam or spray foam, the code requires a minimum of R-10 insulation on your basement walls.
The reason? Energy modeling has shown that such insulation is cost-effective. Energy savings more than justify the investment.
So, here's what you do: remove the fiberglass batt insulation. Air seal leaks in the basement ceiling if you like -- but more importantly, do a good job of air-sealing the rim joist area, as well as the crack between the basement slab and the basement walls. If you have a sump, get an airtight sump lid.
Be sure you have managed bulk water entry through your walls with the usual measures. Then you can insulate your basement walls with rigid foam or spray foam.